This application incorporates by reference of Taiwan application Serial No. 90110879, filed on May 7, 2001.
1. Field of the Invention
The invention relates in general to an ink injector, and more particularly to an apparatus for using bubble as a virtual valve to eject ink and a fabricating method thereof.
2. Description of the Related Art
Over the years, electronic related industries have progressed as the technology advances. For various electronic products, such as computer systems, computer peripherals, appliances and office machines, their functions and appearances have improved greatly as well. For example, in the 1980s, impact-type dot matrix printers and monochrome laser printers were pre-dominant. Later in the 1990s, monochrome inkjet printers and color inkjet printers became popular for general-purpose use while color laser printers were available for professional use. For general use, users would probably choose color inkjet printers after considering the printing quality and price. Users with sufficient budgets would probably purchase a monochrome laser printer. Since the price and quality are critical to the users"" decisions, printer manufacturers aggressively develop their products so that the products have lower cost and better quality, in order to increase the popularity and profit of their products. Therefore, developers are focusing on how to improve the performance of products under limited cost.
Most inkjet printers now use either a bubble inkjet printhead or a piezo-electrical inkjet printhead to eject ink droplets onto a recording medium, such as paper, for printing. The bubble inkjet printhead comprises a plurality of chambers adjacent one another. Each chamber comprises at least a heater, ink, and an orifice. Also, a manifold is adjacent to and in flow communication with the chamber. Ink from a reservoir is supplied to each chamber by passing through the associated manifold. The heater heats the ink of the chamber to create bubbles until the bubbles expand enough to expel the ink droplets through the orifice and onto the recording medium, such as a sheet of paper. When the activation of the heater is terminated, the bubbles collapse so that the ink in the reservoir refills into the chamber through the manifold. Adjusting the concentrations and locations of the droplets on the paper can form a variety of texts and graphics. The quality of the printing result is related to the resolution provided by the printer. Currently, entry-level color printers provide a good resolution of 720xc3x97720 dpi (dots per inch) or 1440xc3x97720 dpi. The finer size the droplet is, the higher resolution the printer has.
However, those bubble inkjet systems (also known as thermally driven bubble system) suffer from cross talk and satellite droplets. When the bubbles expand, the ink is pushed from all sides, so the ink in the chamber is not only ejected through the orifice, but is also pushed towards the manifold. Such effect will deteriorate the ink stability of the adjacent chambers. If the adjacent chamber with unstable ink performed ink ejection, some problems may arise. For example, the size of droplets may vary, or the droplets may hit the paper surface at slightly different locations. After the bubbles collapse, the refilling of the ink into the chamber may also interfere with the ink in the adjacent chambers. The phenomena described above are known as cross talk. Cross talk frequently occurs when the chambers are placed in arrays with close pitch, and the droplets eject from the adjacent orifices. Moreover, the unstable ink condition may affect the ink ejected through the orifice, causing satellite droplets. For example, the ink close to orifice could overflow, or the tail of ink droplet would not be cut off abruptly. The tiny ink droplets that trail the main droplets, known as satellite droplets, may hit the paper at locations slightly different than the main droplets and blur the printed image. The problems of cross talk and satellite droplets degrade the sharpness of printed image. Various technologies have been provided to solve these problems.
Generally, to increase the resolution of the print image, the orifices of the inkjet printhead for ejecting ink from the chamber are arranged in the form of arrays. In practical application, all ink chambers have identical, or very similar, structure; hence, only one ink chamber is illustrated in the following description and related drawings.
FIG. 1 is a cross-sectional view of a known ink chamber on the printhead (disclosed in U.S. Pat. No. 4,494,128), wherein the printhead is particularly applied in a gray scale inkjet printer. An ink reservoir and a vehicle reservoir (not shown in FIG. 1) are used for storing undiluted ink 10 and appropriate diluting vehicle 12, respectively. Also, the ink reservoir and the vehicle reservoir are connected to a chamber 18 by ink capillary 14 and vehicle capillary 16, respectively. The vehicle 12 can be a solvent employed to dissolve the dye in the undiluted ink 10. Varying the ratio of the ink 10 and vehicle 12 produces a wide range of ink concentrations. A discharge orifice 22 is formed on the top surface 19 of the chamber 18. Within the chamber 18 is a means of discharging the ink, such as a heater 20, which heats the ink to create the bubble for expelling a droplet 23 through the discharge orifice 22. The ink valve 24 and vehicle valve 26 are resistors set in the ink capillary 14 and vehicle capillary 16 for controlling the volume of ink 10 and vehicle 12 entering into the chamber 18. When an electrical current is applied to the resistors, the valve bubble is generated in the ink capillary 14 and/or in the vehicle capillary 16 to stop the flow of ink 10 and/or vehicle 12 to enter the chamber 18. The ink valve 24 and vehicle valve 26 can be turned on or off independently for any desired length of time. By appropriately determining the ratios of on/off times of the ink valve 24 and the vehicle valve 26, a full gray scale range of printing is produced. This conventional method creates a narrow region in which a heater is placed. The bubble generated from the heater is able to block the flow of ink 10 or vehicle 12, in order to reduce the effects of cross talk. However, after the droplet 23 has been ejected, the narrow region makes it difficult to refill the chamber 18 with the ink 10 and/or vehicle 12 quickly.
FIG. 2 is an enlarged view of another known ink chamber on the printhead (disclosed in U.S. Pat. No. 5,278,584). There is a discharge means such as the heater 32 on the substrate 29 of the chamber 30. By applying the electrical current to turn on the heater 32, the bubble is generated to expel the ink out of the orifice 34. Subsequently, the chamber 30 is refilled by capillary action. The ink stored in the reservoir flows through the manifold, the channel 36, and the chamber 30, as shown by the arrow A.
According to this conventional method, the channel 36 between the manifold and the chamber 30 has a buffering effect on the ink in the chamber 30. For example, the variation in ink pressure, due to ink ejection or bubble formation, can be blocked by the channel 36. Therefore, the interfering effects of cross talk on the adjacent chambers, caused by the ejection of ink, can be reduced. However, the rate of refilling ink to the chamber 30 is subject to the cross-sectional area of channel 36, and the ink jet frequency of the printer is decreased.
In other words, in FIG. 2 when the bubble is generated and collapsed, the cross talk effects caused by the disturbed flow of ink can be reduced by building a channel between the manifold and the chamber. However, the existence of the channel also prolongs the time for refilling the chamber with ink.
Accordingly, the main goals for researchers and manufacturers are to prevent the cross talk phenomena, increase the flow rate of ink to refill the chamber, and enhance the resolution of inkjet printing. In reference to U.S. Pat. No. 6,102,530 (which is also assigned to the same assignee as the present application), it is described that setting two heaters on two sides of an orifice not only functions as virtual valve but also increases the refill rate of ink.
FIG. 3 is a cross-sectional view of another known ink chamber on the printhead. The manifold 42 is adjacent to and in flow communication with the chamber 40. Ink from the reservoir (not shown) is supplied to the chamber 40 by passing through the manifold 42. Also, the ink is ejected through the orifice 46 that is formed on the top surface 45 of the chamber 40. The discharge resistors, such as the first heater 48 and second heater 50, placed on the opposite sides of the orifice 46 possess different resistances and are electrically connected to a common electrode (not shown) for activating the ink in the associated chamber 40.
After a common electrical pulse is applied, the first heater 48 and second heater 50 are activated simultaneously. Due to the resistance difference, the first heater 48, having a narrower cross-section, is activated more quickly and generates a first bubble 52. The expanding first bubble 52 begins to restrict the ink flow to the manifold 42, and finally functions as a virtual valve to isolate the chamber 40 and to prevent the adjacent chambers from cross talk. Then, a second bubble 54 is formed by the second heater 50. As the second bubble 54 expands and approaches the first bubble 52, the ink 44 is pressurized by the first bubble 52 and second bubble 54 and is ejected through the orifice 46 in the direction F, thereby forming a droplet 56. Following the ink ejection, the first bubble 52 and second bubble 54 begin to collapse in the direction P, thereby allowing ink 44 to refill the chamber 40 through the manifold 42 in the direction shown by the arrow R. Accordingly, the first bubble 52 functions as a virtual valve and prevents the cross talk problem. The refill rate of ink is increased by designing a chamber 40 without a narrow channel. However, there is still a drawback in the manufacture of this printhead. During the manufacturing process, the silicon substrate is anisotropically etched to form the manifold 42 and chamber 40. Therefore, the etching process has to be carefully controlled. In addition, a support layer 58 has to be constructed on the top of the chamber 40 for placing the heaters. It is critical to control the construction of the support layer 58, in order to meet the high requirements of production yield and durability.
Accordingly, to increase production yield and enhance market competition, there is a need for researchers to minimize cross talk and its related effects, and to increase the ink-refill rate without further complicating the manufacturing process.
It is therefore an object of the invention to provide an apparatus and method for using the bubble as a virtual valve to eject ink, in order to reduce the cross talk effects, increase ink-refill rate, and also fabricate the inkjet cartridge with high production yield and durability by a simpler manufacturing method.
According to the objective of the invention, an apparatus for using the bubble as a virtual valve to eject ink is provided. The said apparatus comprises a chamber, orifice, and heater. The chamber is connected to the ink reservoir by a manifold, so that the ink can flow into the chamber through the manifold. An orifice for ejecting ink is located on the top surface in ink communication with the chamber. The chamber has a top surface and a bottom surface. Two heaters are located on the bottom surface of the chamber, wherein one heater is located near the manifold and the other is located away from the manifold. These two heaters are connected in series to a common electrode. In addition, the heater closer to the manifold has a smaller cross-section and consequently has a higher resistance. When an electrical pulse is applied to activate the heaters, the heater closer to the manifold heats up first, and generates a first bubble to isolate the ink flow between the chamber and the manifold. Subsequently, the other heater, which is located away from the manifold, generates a second bubble to pressurize the ink in the chamber with the first bubble, thereby the ink is ejected through the orifice and forms an ink droplet. Then, the first and second bubbles collapse, and remove the isolation between the manifold and the chamber. The ink in the manifold immediately refills the chamber.
In the invention, the first bubble generated by the heater closer to the manifold functions as a virtual valve to isolate the manifold and chamber, so that the cross talk effects on the adjacent chambers can be reduced. Also, the channel between the manifold and the chamber is wide enough so the ink can refill the chamber very quickly. Thus, cross talk is decreased and the printing speed can be increased. Moreover, according to the fabricating method of the invention, the heaters are formed in the bottom surface of the chamber by deposition, so that the components in the chamber are easily constructed and the thin plate, having the orifice, spans the chamber without any burden. Therefore, the production yield and durability are greatly increased.